Wireless computer networks have been defined in which a wireless communication device communicates with a network via an access point.
When a wireless communication device (also referred to as a “station” or “node”) wants to access a WLAN, for example after power-up, sleep mode, or moving to a new area, the wireless communication device searches for access points (APs) by scanning. The IEEE 802.11 standard defines both passive and active scanning. As used herein, “IEEE 802.11” refers to a set of IEEE Wireless LAN (WLAN) standards that govern wireless networking transmission methods. IEEE 802.11 standards have been and are currently being developed by working group 11 of the IEEE LAN/MAN Standards Committee (IEEE 802). Any of the IEEE standards or specifications referred to herein are incorporated by reference in their entirety and may be obtained by contacting the IEEE at IEEE, 445 Hoes Lane, PO Box 1331, Piscataway, N.J. 08855-1331, USA.
In passive scanning, the wireless communication device scans individual channels for beacon frames that are periodically transmitted by the AP. The beacon frame includes synchronization information, and other information about the access point including service set identifier (SSID), supported data rates, etc.
Active scanning is optional, and differs from passive scanning in that the wireless communication device tries to locate access points and initiates the scanning process by broadcasting a probe request frame. Active scanning enables a wireless communication device to receive immediate response from access points, without waiting for transmission of a beacon frame. A probe request frame may include an SSID, or can have a null SSID or can include a destination address of a specific AP. When the probe request frame includes an SSID, all APs with a matching SSID that receive the probe request frame will respond by transmitting a probe response frame. When the probe request frame includes a null SSID, all APs that receive the probe request frame will respond by transmitting a probe response frame. When the probe request frame includes a destination address of a specific AP, only the AP indicated by the destination address will transmit a probe response that will be heard by the wireless communication device.
When the wireless communication device receives a beacon frame it can record information associated with the beacon frame (e.g., corresponding power level and received signal strength) and subsequently use this information to select which access point to communicate through. At the conclusion of the scanning, the wireless communication device (WCD) generates a scan report that includes parameters for each of the APs that were detected during scanning. For each AP detected the scan report can include a number of parameters.
When an authentication process is complete and the wireless communication device is authenticated with the AP, the wireless communication device must associate with the access point before sending data frames. The association process involves the exchange of information about capabilities of the wireless communication device and the AP. Association is necessary to synchronize the wireless communication device and access point with important information, such as supported data rates. The wireless communication device initiates the association by sending an association request frame containing elements such as SSID and supported data rates. The access point responds by sending an association response frame containing an association ID along with other information regarding the access point. Once the wireless communication device and access point complete the association process, they can send data frames to each other.
When the wireless communication device moves about the wireless network or “roams,” the wireless communication device can often benefit from associating with and communicating through a different access point even though the wireless communication device is still within communication range of its current serving access point that it is currently associated with. To decide which AP the wireless communication device should join (or “roam to”) and authenticate and associate with as the wireless communication device moves about the network, the wireless communication device implements an AP selection or “roaming algorithm” to make this decision. The IEEE 802.11 standards do not specify a standard roaming algorithm. Instead, the AP selection or roaming algorithms are left to the discretion of the wireless communication device vendor and are thus usually vendor specific. Many AP selection or roaming algorithms rank APs using one or more performance metrics, such as a Received Signal Strength Indicator (RSSI) that reflects signal strength of a beacon frame received from the AP, and then select the highest ranked AP as the AP to roam to.
Accordingly, it is desirable to provide improved AP selection techniques for use by a wireless communication device as the wireless communication device encounters different APs when moving from one physical location to another in a network. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.